1. Field of the Invention
This invention relates to a quadrature demodulator usable in a receiver for a digital phase modulation signal such as a QPSK (quaternary phase shift keyed) signal, a DQPSK (differential quaternary phase shift keyed) signal, or a .pi./4-shift QPSK signal.
2. Description of the Prior Art
Some of prior art quadrature demodulators in receivers for digital phase modulation signals include digital phase comparators which output a pair of signals representing transmitted data. The output signals of the digital phase comparators are processed by analog circuits including low pass filters and sampling devices. Output signals of the analog circuits are converted into corresponding digital signals, from which the transmitted data is recovered.
For high reliability and accuracy in a data demodulating process, it is generally desirable to replace an analog circuit by a digital circuit.